Re: Help on boot manager 'Boot Manager Menu' and direct boot

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Mon, 3 Dec 2018 at 14:45, Laszlo Ersek <lersek@redhat.com> wrote:
>
> On 12/03/18 11:03, Udit Kumar wrote:
> > Hi Laszlo
> >
> >> Are you using the latest edk2?
> > Yes, when I hit the bug, first step was to move to latest edk2. But this didn't helped.
> >
> > I am not sure, why we are keeping PL011 Fifo mode off in default configuration.
>
> Sorry, I don't know: although the subject logic has gone through several
> updates over time, the default that you point out seems to go back to
> commit 051e63bb551a ("ArmPlatformPkg/PL011Uart: Allowed to change UART
> settings in its initialization function", 2012-02-29). And that commit
> doesn't explain the default.
>

The default setting for
gEfiMdePkgTokenSpaceGuid.PcdUartDefaultReceiveFifoDepth is 1 not 0,
and so you will end up with a 1 character FIFO setting. I wonder if we
could improve PL011UartInitializePort () in PL011UartLib to deal with
this better.

Note that this also affects platforms that can switch between DT and
ACPI boot: the same PL011 is described as a 'dumb' SBSA uart in the
latter case, and so it is up to the firmware to configure the UART
FIFO correctly, or you will not be able to use the UART under the ACPI
OS.